Rolling mill control for compensating for the eccentricity of the rolls



Dec. 1, 1970 D. R. HOWARD 3,543,549

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ATTORNEY States Patent 3,543,549 Patented Dec. 1, 1970 3,543,549 ROLLING MILL CONTROL FOR COMPENSATING FOR THE ECCENTRICITY OF THE ROLLS David Robert Howard, Sheflield, England, assignor to Davy and United Engineering Company Limited, Shetlield, Yorkshire, England Filed Nov. 20, 1968, Ser. No. 777,322 Claims priority, application Great Britain, Nov. 21, 1967, 52,853/ 67 Int. Cl. 1821b 37/00 US. Cl. 72-8 7 Claims ABSTRACT OF THE DISCLOSURE The effects of eccentricity of the rolls of a rolling mill are compensated for by comparing a continuous electrical signal which is representative of the variations in rolling load with a second signal which is representative of the gauge variations of the material being rolled in order to produce a signal which is representative of the ratio of the components of the two signals which occur synchronously withone another. The ratio signal is then multiplied by a signal which is representative of the gauge variations of the material entering the mill to produce a further signal which is representative of those variations in the outgoing gauge of the material which are solely attributable to variations in ingoing gauge. This further signal is subtracted from a signal representative of the outgoing gauge variations due to all sources in order to yield a signal which contains predominantly those variations in outgoing gauge which are caused by eccentricity of the rolls. This signal is used to continuously adjust the roll gap of the mill in such a sense as to diminish the effects on the material being rolled of the eccentricity of the rolls.

This invention relates to rolling mills and in particular to a method of, and apparatus for, removing the elfect of eccentricity and/or ovality of the rolls of rolling mills for plates, sheets and strips.

All rolls for rolling mills are eccentric to some degree i.e. however carefully a roll is ground, the roll barrel is eccentric with respect to the roll necks by which the roll is rotatably supported in use. Additionally, all roll bodies depart to some degree from right circular cylinders. If this departure takes the form of a difference in diameters measured through the geometric centre of the roll body the effect is described as ovality. Eccentricity may also be caused by variations in the metallurgical structure of the roll. It can also arise from variations in the temperature of the roll body caused for instance by the demands of rolling practice. Thus its magnitude and position may vary with time. Nor can it always be completely defined by metrology for if it has its source in a structural defect in the roll this would only appear when the force response of the rotating roll body was examined in the rolling mill. Eccentric movement of a roll and ovality of a roll causes the material to be rolled with a gauge which varies cyclically over its length. The degree to which the eccentricity of the rolls of a rolling mill is reflected in cyclic gauge variations in the rolled material is dependent on the stiifness of the mill itself and on the hardness of the material being rolled in that mill.

It is well known to provide a rolling mill with automatic gauge control means by which the gauge of the material leaving the mill rolls is automatically adjusted to take into account variation in the gauge of the material entering the roll gap. A particularly eflicient type of automatic gauge control is known as a Gaugemeter and works on the principle that the size of the roll gap is equal to the thickness of the outgoing material and by establishing the size of the roll gap, compensatory action can be taken to automatically control the gauge within narrow limits in response to variations in the gauge of the material entering the roll gap. The size of the roll gap is determined by measuring the rolling load on the mill and variations in the rolling load are used to either vary the roll gap by, say, adjusting screwdowns, or to vary the tension in the material being rolled. Variation in the rolling load may however be due to factors other than variations in the gauge of the ingoing material, such factors as for example, eccentricity and ovality of one or more 7 of the rolls of the mill and when automatic gauge control is used which depends for its operation on variations in the rolling load, compensatory forces for a change in rolling load due to the eccentricity or ovality are provided by the control but the compensatory forces act in a direction which instead of diminishing the effects of eccentricity and ovality of the rolls in fact accentuates the eifects on the material being rolled of these undesirable features. If the gauge of the material entering the rolls of a rolling mill provided with automatic gauge control increases, the rolling load increases and a signal is initiated which actuates the roll screws or other means so as to reduce the roll separation. If however the rolling load increases due not to an increase in the gauge of the ingoing material but due to eccentricity or ovality of the rolls, the signal which is initiated must act so as to increase the roll gap otherwise the effect of the eccentricities of the rolls on the material in the roll gap will be accentuated.

It is an object of the present invention to provide a method of, and apparatus for, controlling a rolling mill in which the effects of eccentricity and/or ovality of the mill rolls are diminished.

According to a first feature of the invention in a method of controlling a rolling mill an electrical signal proportional to the variations in rolling load is continuously compared with an electrical signal which is proportional to the gauge variations of the material entering the roll gap to produce a signal proportional to the ratio between the signals, the ratio signal is multiplied by a signal proportional to the ingoing gauge variations to produce a further signal proportional to those variations in outgoing gauge which are solely attributable to variations in ingoing gauge, the further signal is subtracted from a signal proportional to outgoing gauge variations from all sources to yield a signal which contains predominantly those variations in outgoing gauge caused by eccentricity and/or ovality in the rolls and this signal is used to continuously control means for adjusting the roll gap of the mill in a sense to diminish the effects on the material being rolled of eccentricity and/ or ovality of the rolls.

According to a second feature of the invention apparatus for controlling a rolling mill comprises means for obtaining a first electrical signal which is proportional to the variations in the rolling load, means for obtaining a second electrical signal which is proportional to variations in the gauge of the material entering the roll gap, a correlator for synchronously comparing the second signal with the first signal to produce a ratio of these signals, means for multiplying the ratio signal by the second signal and means for subtracting the modified signal from the first signal to produce a signal which contains predominantly those variations in outgoing gauge caused by eccentricity and/or ovality of the rolls and means controlled by this signal to vary the roll gap of the mill in a sense to diminish the eifects on the material being rolled of eccentricity and/ or ovality of the mill rolls.

The first signal which is proportional to variations in the rolling load is conveniently obtained from a load cell positioned between one of the mill rolls in the mill housing and the second electrical signal is conveniently produced by a device mounted upstream of the mill and which produces a signal proportional to the variations in gauge of the material at the point. This signal is delayed by an appropriate amount so that the second signal is proportional to the variations in gauge of the material positioned between the rolls of the mill when the first signal is produced. The roll gap is conveniently adjusted by means of a hydraulic generator which feeds fluid under pressure to a piston cylinder assembly acting between a roll of the mill and the mill housing.

A rolling mill controlled in accordance with the present invention may also be provided with automatic gauge control means which are capable of bringing about a compensatory variation in the roll gap and/or the tension of the material being rolled when a change occurs in the rolling load.

Variations in the roll gap brought about by the automatic gauge control means act in the opposite direction to the variations in the roll gap produced by the control means in accordance with the present invention to diminish the effects on the material being rolled of eccentricity and/ or ovality of the mill rolls.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawing which illustrates diagrammatically a rolling mill provided with automatic gauge control means and control means in accordance with one embodiment of the present invention.

A four-high rolling mill for rolling plate, sheet or strip has a pair of work rolls 1 and 2 which are backed up by massive back-up rolls 3 and 4 respectively. The rolls are mounted at each end in bearing chock arrangements (not shown) and the chocks at one end of the rolls are mounted in a window 5 in a stiff housing 6. The chocks at the other ends of the rolls are mounted in a similar housing (not shown). A load cell 7 is positioned between the upper back-up roll 3 and the housing 6 and a piston and cylinder arrangement 8 is located between the lower back-up roll 4 and the housing 6. The piston and cylinder arrangement is supplied with fluid under pressure from the hydraulic generator 9 which is driven by a motor 10. The material being rolled, conveniently strip, is fed from an uncoiler 11 positioned on one side of the mill housing, between the work rolls 1 and 2 onto a coiler 12 positioned on the other side of the mill housing. The uncoiler 11 is driven by an electric motor 13 which controls the back tension in the strip. A gaugemeter 14 receives an electrical signal from the load cell 7 via conductor 15 and supplies an electrical signal to the motor 13 by conductor 16 and also supplies a further electrical signal to the hydraulic generator 9 via conductor 17. As a check for the accurate operation of the gaugemeter, the

gauge of the material downstream of the rolling mill is continuously measured by any convenient means 18 and a signal is supplied to the gaugemeter to continually correct the meter.

Means 19 for producing an electrical signal which is proportional to the variations in gauge of the ingoing strip is located upstream of the rolling mill and the signal is supplied to a delay unit 20 and from the delay unit to a correlator 21. The delay provided by the unit 20 is equal to the period of time taken for the strip to travel from the unit 19 to the rolls of the mill. The load cell 7 also provides an electrical signal which is proportional to the rolling load to a unit 22 which modifies the signal according to the mill modulus. The output from this unit is also applied to the correlator 21.

The correlator 21 only compares those variations in the two incoming signals which occur synchronously with one another and the output signal from the correlator is proportional to the ratio of the synchronously occurring components of the signal from the unit 22 and the signal from the delay unit 20. This ratio signal is multiplied in the device 21' by the signal from the delay unit 20 which is proportional to the ingoing gauge variations to identify those variations in outgoing gauge which are solely attributable to variations in ingoing gauge and the output from the device 21' enters one input of a comparator 23 which also receives an input signal from the unit 22. In this comparator the modified signal from the correlator is subtracted from the signal from the unit 22 and the output signal which contains predominantly those variations in outgoing gauge caused by eccentricity and/or ovality in the rolls is applied to a plurality of further circuit arrangements 24. Only one of the further circuit arrangements 24 is shown and this circuit arrangement receives two signals from a generator which is rotated by the back-up rolls 3. The two signals are the sine and cosine waves respectively of the same frequency as the angular rotation of the rolls 3. These signals are adjusted in phase and amplitude in the circuit arrangements 24 and signals representative of the amplitude and phase of the eccentricity and/or ovality of roll 3 are applied to an amplifier 25. At least one and preferably both of the two back-up rolls 3 and 4 are provided with generators and circuit arrangements 24 and the output from each of the circuit arrangements are applied to the amplifier 25 to control the output from the hydraulic generator 9. The circuit arrangements are described in more detail in our co-pending British application No. 7,483/ 66.

The electrical signal from the load cell 7 is proportional to the rolling load in the mill and the variations in the rolling load are due to several factors including variation in the gauge of the strip entering the mill, variations due to the hardness of the material entering the mill, and variations due to eccentricity and ovality of the rolls of the mill. This signal is applied to the gaugemeter 14 and in the absence of the circuitry in accordance with the present invention the gaugemeter unit 14 would attempt to compensate for all the variations in the rolling load by varying the pressure provided on the rolls by hydraulic generator 9 and/or vary the back tension in the material passing through the mill. The modified signal entering the comparator 23 from the device 21 is proportional to the variations in the gauge of the strip leaving the mill which are due to the variations in the strip entering the mill and the signal entering the comparator from the unit 22 is proportional to the variations in the gauge of the material leaving the mill due to the variations in the gauge of the material entering the mill, the hardness of that material, the friction between the rolls of the mill and the eccentricity and ovality of the mill rolls. The first signal is subtracted from the second signal in the comparator 23 leaving a dilference signal which is proportional to the variations in the gauge of the outgoing material due only to the variations in the hardness of the ingoing material, the friction between the rolls, and the eccentricity of the rolls. The output signal from the comparator is applied to each of the further circuits 24 and each of these circuits receives signals from a dilferent roll of the mill.

The circuits 24 are only atfected by the components in the signal applied to them from the comparator 23 which are caused by roll eccentricity and/or ovality and are therefore of the same frequency as the sine and co-sine signals received from the mill roll with which each circuit is associated. This assumes that variations in hardness of the ingoing material and the frictional coefficient are never of the same frequency as those in the gauge variation of the ingoing material and the eccentricity of the rolls.

The sum of the output signals from the circuits 24 are applied to the amplifier 25 which drives the hydraulic generator 9 in a sense to completely cancel load variations at the roll gap caused by eccentricity and/ or ovality in the rolls.

By this invention therefore the effects of eccentricity and/or ovality in the mill rolls on the material in the roll gap are substantially reduced to zero and the variation in the roll gap depends entirely on and corrects for the variation in the properties of the ingoing strip. This obviously will result in a more uniform and more acceptable rolled product from the mill.

The invention may also be applied to a tandem mill having a plurality of mill stands. In the accompanying drawing the recoiler 12 could easily be replaced by a second stand. The signal (P+AP) emanating from the load cell 7 of the first stand would give an accurate measure of the strip thickness arriving at the second stand which would itself be fitted with load cells so that a further pair of signals constituting the ingoing thickness at the second stand would be available. By delaying the thickness variation signal from stand 1 until it synchronised with the thickness variation from stand 2 a further correlator and eccentricity compensation circuit for stand 2 and so compensate for eccentricity and ovality of the rolls of the second stand. This procedure could of course be continued for all stands of a multi-stand tandem mill. With this arrangement the only measurement of strip thickness required is at the ingoing side of the mill train where the strip is thick and is moving relatively slowly and where the measurement can be made easily. Each of the mill stands of the mill train could be provided with an automatic gauge control system if required. A particular feature of this invention when applied to multi-stand mills is that the roll gap of one mill stand with rolls compensated for eccentricity and/or ovality may be used to trigger the circuit for the eccentricity compensation of the succeeding stand.

What I claim is:

1. A method of automatically controlling a rolling mill, comprising the steps of producing an electrical signal representative of the variations in rolling load of the mill, producing an electrical signal which is representative of the gauge variations of the material entering the roll gap comparing said signals to produce a signal representative of the ratio of the components of the signals which occur synchronously with one another, multiplying the ratio signal by a signal representative of the gauge variations of the material entering the roll gap to produce further signal representative of those variations in the outgoing gauge of the material which are solely attributable to variations in ingoing gauge, substracting said further signal from the signal representative of the outgoing gauge variations due to all sources to yield a signal which contains predominantly those variations in outgoing gauge caused by eccentricity in the rolls and continuously controlling by the last-mentioned signal the adjustment of the roll gap of the mill in a sense to diminish the eliects on the material-being rolled of eccentricity of the rolls.

2. In a rolling mill having a pair of work rolls and means for adjusting the roll gap between the work rolls, an automatic control system comprising means for obtaining a first electrical signal which is representative of the variations in the rolling load of the mill, means for obtaining a second electrical signal which is representative of the gauge variations of the material entering the roll gap, means for continuously comparing the first and second signals and for producing a ratio signal representative of the ratio of the components of the first and second signals which occur synchronously with one another, means for multiplying the ratio signal and the second signal together to produce a modified signal, means for subtracting the modified signal from the first signal to produce a further signal which contains predominantly those variations in the outgoing gauge of the material caused by eccentricity of the rolls and which signal is applied to said means for adjusting the roll gap in a sense to diminish the etfects on the material being rolled of eccentricity of the mill rolls.

3. An automatic control system as claimed in claim 2 in which at least one of the rolls has associated therewith circuit means to which said further signal is applied and which identifies the component of the further signal which is caused by eccentricity of that roll and controls said means for varying the roll gap of the mill in a sense to diminish the effect on the material being rolled of the eccentricity of that roll.

4. An automatic control system as claimed in claim 3 in which said roll drives generator means which produce sine and cosine signals of the same frequency as the angular rotation of the roll and said signals are applied as reference signals to respective phase sensitive detectors forming part of said circuit means, which detectors also receive said further signal.

5. An automatic control system as claimed in claim 2 in which the means for obtaining the second signal is a gauge measuring device positioned upstream of the roll gap for continuously measuring the gauge of the material at that position and a delay circuit for delaying the signal from the gauge device by an amount equal to the time taken for the material measured upstream of the roll gap to travel to the roll gap.

6. An automatic control system as claimed in claim 2 including gauge control means for controlling the adjustment of the roll gap of the mill in accordance with variations in the properties of the material entering the roll gap.

7. In a rolling mill having a pair of work rolls, each work roll having a back-up roll associated therewith, said rolls being supported at their ends in rigid housings, a piston cylinder assembly acting between one of the backup rolls and the housing and fed with fluid under pressure from a hydraulic generator to adjust the gap between the work rolls, an automatic control system comprising a load cell positioned between one of the back-up rolls and the mill housing for continuously providing a first electrical signal which is representative of the variations in the rolling load of the mill, means for obtaining a second electrical signal which is representative of the gauge variations of the material entering the roll gap, correlator means for continuously comparing the first and second signals and for producing a ratio signal representative of the ratio of the components of the first and second signals which occur synchronously with one another, means for multiplying the ratio signal and the second signal together to produce a modified signal, means for subtracting the modified signal from the first signal to produce a further signal which contains predominantly those variations in the outgoing gauge of the material caused by eccentricity of the rolls, at least the back-up rolls having associated therewith circuit means to which said further signal is applied and which circuit means identifies the component of the further signal which is caused by the eccentricity of the back-up rolls and controls said piston cylinder assembly in a sense to diminish the effect on the mzlilterial being rolled of the eccentricity of the back-up ro s.

References Cited UNITED STATES PATENTS MILTON S. MEHR, Primary Examiner US. Cl. X.R. 7216 

